This invention relates to recovery boilers, and more particularly to devices and methods for cleaning the smelt spouts of recovery boilers.
A recovery boiler is used in the craft pulping process to burn the waste product that is generated when wood chips are converted to paper pulp. The waste product, called “black Liquor”, is removed from pulp and pumped into a recovery boiler where it is burned. This combustion not only creates steam, which is used as an energy source, but also renders the black liquor down to its basic chemical elements, called smelt. The smelt, a mixture of molten sulfur and salts, decants from the bottom of the recovery boiler (at a temperature of approximately 1,600 degrees F.) through troughs located at the bottom of the boiler. These troughs are called smelt spouts. The smelt decants from the spouts, is hit with a scatter jet of steam or the like to help break the smelt into smaller size particles, which fall into a dissolving tank where it is mixed with warm water and subsequently referred to as green liquor. The green liquor is reconstituted, or fortified with more chemicals making it white liquor which is then placed back into a digester where it is mixed with woodchips to make more pulp and consequently transformed back into black liquor completing the cycle of green, white, and black liquor with smelt as an interim step between black and green.
The liquid smelt will solidify quite readily at temperatures below 1200 degrees F. and therefore, smelt as it decants from the smelt spout can and will become solid, restricting the flow of liquid smelt through the spouts. Traditionally the spouts have been kept flowing and operational by the boiler operations staff who periodically (approximately two to four times a shift (a shift might typically be 8 hours)) clean the spout trough and opening by scraping the spout with long lance type tool. A single boiler may have as many as six or as few as two smelt spouts. The spouts are trough shaped, typically 3-feet in length, about 6-inches inside width with a full radius bottom and extend from the bottom side (where the boiler floor meets the boiler wall) of a boiler at about a 15-degree angle.
Accordingly, there is an opportunity for an automated version of a spout cleaner.